Tires have been a vehicle's most important safety feature for more than 100 years. After all, they are a vehicle's only contact with the road. Even the brawniest engine, strongest brakes, and most advanced anti-skid system are at the mercy of the tire's grip on the road. Every move a driver makes with the steering wheel, brake or gas pedal is transmitted to the road through the four notepad-sized contact patches of the tires.

So, if a consumer has tires that are worn, under-inflated, or not suited to the environment, they put themselves, their vehicle, and others at risk. But most drivers don't know enough about tires to make an educated purchase. For some, the choice comes down to price and availability. Others buy tires based on appearance or reputation.

We've compiled a list of 12 areas you should consider when purchasing new tires. If you're looking to save money, get the best fuel economy, make an informed decision, or buy the best quality tire then this article is for you. This list will cover the basic information you should understand to select the right tires for your vehicle and give you an understanding of how tires function.

Go on to the next page to learn some of the basics about tires.

1

Understand Tire Basics

Simply put, a tire is a flexible container of compressed air. This air container support the vehicle's load; propels a vehicle forward, backward and side-to-side; stops the vehicle; and cushions the load from road imperfections.

Today's tires have between 19 and 25 different components. Tires are built from the inside out rather than the outside in. The heart of every tire is an inner liner. Its job is to give the tire shape and hold in air. Fabric belts are wrapped around the inner liner. The bead is fastened to the bottom of the fabric belts and holds the tire to the wheel.

On top of the fabric belts are steel belts. These belts have two jobs: They give the tire stability and make the tread pattern as flat as possible. (A flatter tread means more contact with the road.) The tire tread is on top of the belts. There are different tread patterns for different types of tires. The sidewall on the side of the tire gives it stiffness and ride characteristics. A taller, softer sidewall will absorb more bumps, while a shorter, stiffer sidewall will provide better cornering ability and sharper steering response.

On the sidewall of every passenger-car and light-truck tire is an alphanumeric code that describes the dimensions of the tire. For most tires, this code will start with a "P." Some may start with an "LT" to signify light truck. Some tires may have a "Max. Load" indication. When selecting new tires, it is important to make sure a tire's load rating is at least a high as the tire you are replacing.

On the next page we'll talk about how to choose the right tire.

2

Choose the Right Tire

Not all tires are created equal -- make sure you choose the right tire for your car or truck.

Perhaps the biggest mistake a consumer can make when replacing tires is not using the correct size. On the sidewall of your tire, you'll find a code that tells the tire's size and capabilities. Here's a sample code:

P195/60R16 63H M+S

P - Type of tire

195 - Width of the tire across the tread in millimeters

60 - Aspect ratio of the sidewall compared to the width

R - Radial construction

16 - Diameter of the rim in inches

63 - Tire's load rating

H - Tire's speed rating

M+S - Tire is suitable for all-season driving

If the tire-size code starts with LT instead of P, it means the tire is a light-truck tire. Light-truck tires are designed to have higher-load carrying capacities and are usually found on pickups and SUVs. These vehicles are not required to have LT tires, and in many cases, the original-equipment specification calls for passenger-car tires.

The speed rating translates into the tire's ability to dissipate heat, or prevent heat build-up. Heat is a tire's enemy. The more heat, the faster the tire wears, and the faster a tire might break down. A tire with a higher speed rating can dissipate more heat on long highway trips. If a consumer were to spend little time on the highway, the speed rating might not be an important factor in choosing a replacement tire.

Tires are speed rated from 99 to 186 miles per hour (159.3 to 299.3 kilometers per hour). The most common speed ratings are T (118 miles per hour or 189.9 kilometers per hour) and H (130 miles per hour or 209.2 kilometers per hour). Both of those ratings clearly exceed the nationally posted speed limits and would make excellent long-distance highway tires. If a consumer were to drive only in urban situations at low speeds, a tire with an S (112 miles per hour or 180.2 kilometers per hour) speed rating might be completely acceptable.

Another important factor in choosing a replacement tire is the load rating. The load capacity number on the tire-size code indicates the load-carrying capacity of that single tire. When selecting replacement tires, consumers have to be careful not to select a tire with a lower load-carrying capacity.

Regardless of a tire's speed rating, load-carrying ability, size and construction, traction are the keys to safety. A common mistake is to select a tire without considering its ability to hold the road. Savvy consumers will balance a tire's traction in dry conditions, in wet conditions and in the snow. If you desire a high-performance tire but live in northern climates, consider a "winter" tire for driving in the snowy season. If you live where the weather is warm all year, a touring tire may suit your needs just fine.

Most consumers will make the mistake of waiting until spring to get new tires. As a tire wears out, dry traction generally increases and wet and snow traction decrease. So the best time to buy new tires is not in the spring, but in the fall.

Passenger-car and light-truck tires are very different. Pickup and SUV owners will generally select passenger-car tires because they are less costly and offer a smoother ride. However, if a vehicle will consistently be loaded with cargo or will be asked to pull a heavy trailer, then perhaps the higher load-carrying capacity of a light-truck tire would be the better choice.

Go on to the next page to learn where to buy your new tires.

3

Know Where to Buy

When it comes time to get a set of new tires, drivers have a lot of options. Traditionally, the most expensive option is to return to the dealership. Dealers will replace worn tires with original-equipment tires. This option can cost twice as much as going to the local shop down the street.

That local shop, be it a national chain or mom-and-pop establishment, is probably the best place for the average consumer to shop for new tires. Prices can be reasonable and the service manager will help consumers select the correct tire for their vehicle. However, consumers should always shop around for the best prices. Tire and installation prices vary widely from store to store.

Another option is the discount tire retailer. These wholesale tire distributors sell tires at extreme discounts. In addition to low prices, they are often just a phone call or a mouse click away. However, when consumers purchase tires from the discount retailer, the tires are shipped to the consumer's door. It is up to the consumer to find a local shop to balance and mount the tires. (In some cases, these tire retailers will offer discount mounting and installation at a local tire store.) For some people who want exclusive or hard-to-find tires, this is the only option.

If you purchase your tires online, you'll need to do a little extra research to find out how much it'll cost to have them put on your vehicle. A local shop will charge you to mount and balance the tires, as well as any other additional fees, such as disposing the old tires. Call around to several shops to get their full price for putting on your new tires.

On the next page we'll learn how your driving habits should be factored into your tire purchase.

Regardless of where you get new tires, there are a few things you should keep in mind:

Know the size and type of tire recommended by your owner's manual.

Determine your needs and priorities. What type of driving you will be doing? Do you prefer a soft ride, a firm ride, or a mix of the two?

Make sure you purchase a tire that is capable of supporting the load your vehicle might demand. Don't buy a passenger-car tire if you need a light-truck tire.

Don't buy more tire than you need. Consumers often overestimate their tire needs. In most cases, a quality all-season tire will suffice where a touring tire might be suggested.

Keep in mind that any tire selection is a balance between ride quality, noise suppression, fuel economy, wear, load capability and cost. It's the job of the tire-store expert and the consumer to select a tire that is the right balance of each.

An interesting trend in the automotive aftermarket industry is "plus sizing." It involves mounting bigger wheels and tires on a vehicle to enhance the look or improve handling.

Plus sizing usually increases cornering response and traction. Often these gains come at the expense of increased ride harshness. In addition, these larger wheels and tires are often not as durable as OEM wheels and tires.

A few items of note for consumers considering plus sizing:

Make sure that the tire and wheel are approved for use on your vehicle.

Make sure that the replacement tire has the same load-carrying capacity.

The new wheel and tire combination should be within 3 percent +/- the original tire diameter.

Make sure that a new tire placard is installed to inform future owners of the correct tire pressure.

Go to the next page to learn more about tire technology.

5

Know Your Tire Tech

The biggest change in tire technology is actually a return to the past. Early tires were solid rings of rubber that wrapped around wagon wheels. These tires were hard riding, but also impervious to punctures and very durable -- ideally suited to the rough terrain of the day. Today, tire manufacturers are trying to make the flat tire a distant memory.

Today's run-flat tires contain air and are much more complicated in construction than early rubber rings. But, they operate on the same principle: They are tough enough to run without air if necessary.

The above diagram shows the difference in construction between a conventional tire and a stiff-sidewall run-flat tire. In a stiff-sidewall run-flat tire, there is extra sidewall reinforcing rubber that prevents the sidewall of the tire from deflecting. In an inner-liner run-flat, the sidewall is no stiffer than a conventional tire, but a hard rubber or plastic ring inside the tire helps keep the tire's sidewall from deflecting.

There are two different styles of run-flat tires. The first uses very stiff sidewalls that can support the weight of the vehicle in the event of pressure loss. Several tire companies offer this type of run-flat, and they can typically be driven with no air pressure for about 50 miles (80.5 kilometers) at speeds up to 55 miles per hour (88.5 kilometers per hour). However, most cannot be repaired after being punctured. The sidewalls can't be very tall, so most are low-profile designs. Because of this, they are typically used on sports cars, though they're also available for regular passenger cars and minivans.

The second style is called the PAX system and was invented by Michelin. The PAX system isn't just a tire. It's a tire/wheel package that consists of four components: a tire, a wheel, an inner support ring, and a tire-inflation monitor. If the PAX system tire loses air pressure, it only drops about halfway down. At that point, the underside of the tread rests on an inner support ring that runs around the circumference of the wheel. According to Michelin, the vehicle can be driven for 125 miles (201.2 kilometers) at up to 55 miles per hour (88.5 kilometers per hour).

The PAX system also incorporates a special bead -- the connection between tire and wheel -- that helps lock the tire onto the wheel even if the tire loses air pressure, something traditional run-flat tires -- and regular tires -- don't usually have. Unlike most run-flat tires, the PAX-system tire can be repaired if the hole is in the tread area and less than 1/4-inch (6.4-millimeter) in diameter -- as is the case for regular tires.

Because the sidewalls of an un-inflated PAX tire don't support the weight of the vehicle in the event of pressure loss, the sidewalls can be taller than on run-flat tires. They also don't need to be as stiff, which means that the ride quality is better. This makes the PAX system better suited to SUVs, as well as regular passenger cars and minivans.

Go on to the next page to find out about selecting the right tire for the best fuel economy.

6

Carefully Consider Fuel Economy

Not all replacement tires are designed with fuel economy as high a priority.

Fuel economy can be a major factor for some tire consumers. If you're considering buying a tire that can assist in your vehicle's fuel economy, know that not all tires are made alike. Purchasing a tire that is different than the one you had when the vehicle was new may impact the fuel economy, for good or bad.

According to Bill VandeWater at Bridgestone Firestone North America, "consumers can see a 15 to 20 percent difference in their fuel economy depending on the tire they select." Some studies have shown that many consumers like high fuel economy, but not at the cost of mileage or performance, especially in wet conditions.

Though many consumers consider fuel economy a high priority, it is typically not the number one priority for the consumer. Therefore not all replacement tires are designed with fuel economy as high a priority. According to VandeWater, "If a consumer wants a good fuel economy tire, the best choice is usually the original equipment tire."

California and the federal government have passed laws to label tires by their fuel efficiency but, according to an L.A. Times article, implementing the standards has been difficult and most consumers don't know that tires can positively or negatively impact a vehicle's fuel economy [source: Bensinger].

Consumers should also not forget that fuel economy is also dependant on proper air pressure. Monitoring air pressure regularly, and with proper inflation pressures as dictated by the vehicle owner's manual, is the best route to ensure maximum fuel economy.

On the next page we'll discuss the differences between purchasing new and used tires.

7

New vs. Used Tires

You've probably seen used car tire piles along the side of the road at some point. But should you purchase a used tire to save money and will it hold up as long? Most people opt for new tires, but some look to used tires as a way to save money.

Consider the fact that some retailers have deals where you buy three tires and you get the fourth free. You may not necessarily need to replace that fourth tire, but you do because it's free. Used tires that are only slightly worn, like in this situation, may be a good option to save a little money.

The flip side is purchasing an old or worn out tire that isn't safe. Used tires may have defects, punctures or tread-wear you may or may not be able to see. When considering purchasing a used tire you can test the depth of the tread by using a penny. Simply flip the penny upside down and place it inside each of the tire's tread grooves. If the top of Lincoln's head can be seen from any of the grooves then the tread is too low [source: Consumer Reports].

If the tread is still good, you still need to inspect the tire for any defects. This may be difficult and some problems may not be noticeable until the tire is on the vehicle. Purchasing a used tire that has already been plugged or patched may save money, but is not a good idea. Worn tires will not stop as fast and will be more likely to skid on wet surfaces [source: Consumer Reports].

New tires will come with some type of guarantee or warranty that a used tire will not have. If you want a little piece of mind that your tires are in the best condition possible, buy new ones.

Go on to the next page to find out about how long you can expect your new tires to last.

8

Selecting Tires Based on Tread Wear

A manufacturer's estimate on how long a tire should last is based on their testing and not always on real-world conditions.

Tire longevity is dependent on several factors, which include your driving habits, the elevation of where you live, climate, road conditions and the manufacturer's tire longevity estimate. The harder the road conditions, the faster your tire will wear down.

Curvy roads, pot holes and other road conditions will cause the tread to wear down faster. If you're the type to make long burn-outs on the road, we probably don't have to tell you that your tires won't last as long as they're supposed to either.

The average mileage length for all-season tires is about 40,000 to 100,000 miles (64,374 to 160,934 kilometers) [source: ConsumerSearch]. Other types of tires typically won't last as long. High-performance all-season tires will have a longevity of 40,000 to 70,000 miles (64,374 to 112,654 kilometers) and top-performance tires don't even have a guaranteed tread life and usually don't last more than 25,000 miles (40,234 kilometers) [source: Motor Trend].

A manufacturer's estimate on how long a tire should last is based on their testing and not always on real-world conditions [source: Cook]. To determine how the tires you're purchasing will wear, look for the tire's Uniform Tire Quality Grading, or UTQG. The UTQG is the U.S. Department of Transportation's labeling system for the tread wear, temperature resistance and traction of each type of tire [source: Cook]. A tire with a UTQG tread wear of 300 is predicted to last three times longer than a tire with a UTQG of 100. A scale of A to C is used for temperature ratings, and a scale of AA to C is used for traction ratings.

Although the UTQG can help you compare tire longevity within a single brand, the grading system can be interpreted in different ways between different brands. So using the UTQG between two different brands may not be beneficial [source: Tire Rack].

If you buy an average all-season tire, you can probably expect it to last several years under normal driving conditions and even longer depending on what road conditions you encounter, how you drive and what type of tire you purchase.

On the next page, we'll learn why it's a good idea to use the manufacturer recommended size and tire type.

9

Take the Vehicle Manufacturer's Recommendation

We mentioned earlier that vehicle manufacturers often have a recommended tire size and type for each vehicle. This recommendation is based on the size, weight, load capacity, off-road capability and steering for your specific vehicle. Changing the tire size and type could impact the handling of your vehicle. We talked about how plus sizing a tire can change certain aspects of your driving experience.

Changing the tire size can also affect your speedometer reading. For many cars, the speedometer reading is based on one full revolution of the tire on your vehicle. If the tire size is changed, then the time it takes a tire to make one full revolution will increase [source: Yahoo Autos]. Since the speedometer rating is calibrated for only one length of rotation, a newer tire that is larger will inhibit the speedometer from reading the correct speed of the vehicle.

If you have an electronic automatic transmission, changing your tire size can also impact the timing of your shifts [source: Yahoo Autos]. This may impact your fuel mileage, uphill and downhill transmission changes as well as the general shift timing.

Downsizing your vehicle's tires can also have negative effects as well. It's obvious that the tires on your vehicle are keeping it up off of the ground. Well, the size of those tires is part of the reason why the car doesn't come crashing down. If you tried to put a smaller size tire on your vehicle, you would be adding additional stress to the tire that it may not be able to handle. A smaller sized tire may need a different wheel rim to handle the changes.

You can change the size of the tires on your vehicle but these problems must be factored in and adjustments made so that the vehicle will function correctly with the new tires. Changing the tire diameter or the aspect ratio is possible if you can maintain the correct load capacity and adjust other potential problems, like the speedometer [source: Yahoo Autos].

Up next, find out what you should ask your mechanic to check when you buy a new set of tires.

10

Maintain Your Vehicle

We all know that maintaining a vehicle can be costly, but what's even worse is paying extra money when you could have dealt with a problem earlier. When you get new tires put on, there are several areas that your mechanic can easily get to while your car is on the lift with the tires off.

If you're having problems with your CV joints, tie rods, brakes or any suspension issues, now might be a good time to have some of those problems taken care of. Your auto shop will do an alignment on your vehicle when you get new tires put on, but if you have bad shocks or other suspension problems, it could cause your new tires to wear out a lot faster than they should [source: Fogelson]. Before you know it you could be laying down more money for new tires that could be avoided if you had your suspension problems taken care of originally.

If your shocks, struts and the alignment are all good to go, having your brakes changed before the tires are put on could save you some money. Many shops will charge a flat fee just for looking at your vehicle, but if you get multiple things fixed on the car at the same time, you're only charged once. So if you know your brakes are bad, or that CV joint is clicking loudly when you turn, consider having the work done while you're getting the tires put on. You'll eliminate future problems and you'll save a few dollars in the long run.

Have a trusted mechanic or friend inspect the car to determine what you may need to have fixed. If you can eliminate a suspension problem, you'll help your tires last longer and keep yourself safer on the road at the same time.

Go on to the next page to find out how researching new tires can help you make a better purchase.

11

Read the Reviews

Subscription services like Consumer Reports will break the tire down into categories such as dry braking, wet braking, hydroplaning, tread life, ride comfort and others.

It's easier than ever to find reviews of products before you buy them and tires are no different. Although it may not be as exciting as reading other reviews, doing a little research on your tire purchase can help you get exactly what you want.

Look for information about how the tire may help fuel economy, how long the tire has lasted for other people, how much road noise it makes, how well it handles, and if there are any known problems or potential recalls.

Subscription services like Consumer Reports will break the tire down into categories such as dry braking, wet braking, hydroplaning, tread life, ride comfort and others [source: Consumer Reports]. Information like this will give you a good perspective on the quality of the tire you're purchasing. Compare several types of tires and find the one that matches your needs as well as your budget.

Not all tires will perform the same way when it comes to hydroplaning, braking, cornering, etc. Reading what others have experienced or what experts say about a specific tire will help you make an informed decision when you purchase your tires. Keep in mind that the most expensive tire may not be the best one available.

If you want better tread wear and don't mind extra road noise then you can narrow down your search. Or if you prefer comfort to longevity you can pick out the right tire for you before you buy them online or at the auto shop. No matter what you choose just be sure to do at least a little research beforehand.

It is generally accepted that on front-drive vehicles, where all tires are the same size, you rotate the front tires to the rear in a straight line and cross the back tires to the front. In a rear-drive vehicle, you rotate the backs in a straight line to the front and cross the front tires to the back. On all- or four-wheel-drive vehicles, the rotation pattern most often suggested is a simple "X." The left front and right rear swap places, and the right front and left rear swap places.

Many sports cars and some luxury and sport-utility vehicles have unidirectional tires. Unidirectional tires have tread patterns that are designed to perform in the direction denoted on the tire sidewall only. They should always be rotated front to rear (assuming they are the same size). This ensures that the direction of revolution does not change.

If you are rotating a full-size spare into the mix, it is common practice to put that tire in the right rear. Consumers should consult their owner's manual for the correct tire-rotation procedure for their vehicle.

Proper tire inflation is also important for many reasons:

A properly inflated tire will generate less heat or friction with the road, increasing fuel economy and decreasing tire wear.

A tire that's either over- or under-inflated will wear unevenly.

A tire that is low in pressure loses cornering ability because the sidewall isn't as stiff.

Perhaps more important for SUV and light-truck owners, a tire's load capacity decreases as it loses air pressure. So, if you were to pack your SUV to the rafters for a family vacation without adjusting tire pressures to handle the increased load, you may be asking for trouble. Those under-inflated tires would quickly heat up under the extra load and possibly have a failure, leading to travel time lost fixing a flat -- or worse.

Regardless of temperature, tires lose between 1 to 2 pounds per square inch (psi) per month. In addition, for every 10-degree Fahrenheit (12.2-degree Celsius) drop in temperature, a tire will lose another pound of pressure. So a tire left unchecked from the time it was filled to 35 psi on an 80-degree (26.7-degree Celsius) day in May is down by 12 psi on a 30-degree (-1.1-degree Celsius) day in November. That under-inflation will affect fuel economy and wet traction, and also increase tire wear.

For lots more information about tire buying tips, follow the links on the next page.